The present invention relates to an X-ray CT (computed tomography) apparatus having a multi column X-ray detector or a two-dimensional X-ray detector of matrix arrangement represented by a flat panel X-ray detector and X-ray CT imaging method, as well as to a CT value conversion of pixels in a tomographic image made by a conventional (axial) scan or cinescan or helical scan.
In the conventional technique a multi column X-ray detector type X-ray CT apparatus or an X-ray CT apparatus by a two-dimensional X-ray area detector of matrix arrangement represented by a flat panel, reconstructs a tomographic image Gj (x, y) of row j from the projection data of two-dimensional X-ray area detector of row j, and uses the CT value conversion parameters of the two-dimensional X-ray area detector of row j to perform a CT value conversion after a three-dimensional back-projection process in the three-dimensional image reconstruction as shown in FIG. 15 (c.f., JP-A-2004-073360). However, in the three-dimensional back projection process in the three-dimensional image reconstruction, because the image reconstruction of one single tomographic image uses the projection data derived from a plurality of rows of two-dimensional X-ray area detectors, the difference of characteristics of two-dimensional X-ray area detector in each row may pose a problem if only one row of CT value conversion parameters is used.
In a multi column X-ray detector type X-ray CT apparatus, or an X-ray CT apparatus having two-dimensional X-ray area detectors of matrix arrangement represented by a flat panel, the problem of exposure to unused X-ray tends to aggravate along with the increase of the cone angle of the X-ray cone beam.